[Parametric methods applied to the standardization of gestational reference intervals for blood renin activity,...

This investigation is devoted to define monthly-qualified gestational reference intervals for plasma renin, aldosterone and cortisol as derived by transverse or longitudinal approaches. Reference intervals refer to 95% confidence interval, 90% tolerance interval, the 95% predictive interval, in addition to the mean plus or minus the standard error and standard deviation. By applying both methodological approaches it has been found that plasma renin and aldosterone exhibit a progressive gestational increase. By contrast, cortisol shows an initial increase and thereafter stays on the same values. Statistical analysis revealed the transversally--and longitudinally--derived reference intervals to be not statistically different. Because of such a similarity, laboratory medicine can interchangeably use both kinds of reference intervals for estimating the normality of plasma renin, aldosterone and cortisol values in a single case of pregnancy. This interchangeability of values leads to simplify the methodology for measuring plasma renin and aldosterone in pregnancy since it is not necessary to standardize the gestational nomograms for renin-sodium and/or aldosterone-sodium relationship. This is a real way to reduce the costs and to optimize the compliance in the monitoring of pregnancy.